A bag supply tube of metal for head air bags in an automotive vehicle commonly have at least one end provided with a tube bend for elbows whose free extremity has a circularly cylindrical sleeve-like enlargement which is intended to fit over a connecting fitting, especially a fitting of a gas generator.
Such tubes have been used in practice and may be referred to as a gas lance, being employed to supply the gas to the head air bags of the vehicle. One end of the gas lance is usually closed while the other end is formed directly with the circularly cylindrical sleeve-like enlargement which fits sealingly onto the connecting fitting of a gas generator.
In earlier systems, to provide a sufficient seal and a connection which was to prevent axial shifting as a result of the gas pressure, the connecting fitting of the generator had an outwardly open annular groove in which a portion of the sleeve-like attachment engaged.
The circularly cylindrical sleeve-like enlargement was a component of a 90° tube bend. Since the vehicle generally has little space available to accommodate the air bag and the gas feeder therefor, it has been important to make that 90° tube bend as flat as possible so that the air bag system, as a whole, is comparatively compact. The need for a tight bend has created problems with earlier cold-forming techniques in the fabrication of such units since it was difficult with standard cold-forming approaches to make both a tight bend and a sleeve-like formation thereon. The result in some cases was that the steel of the tube was excessively stressed. The result of that stress was detrimental crack formation, especially of outer parts of the bend and folds at inner parts of the bend.
Accordingly in practice the tube end was initially given a 45° bend with a radius of Bay, 30 mm. The tube end was then subjected to enlargement and then the bend at the same radius of say 30 mm was extended into a 90° bend. In order to keep the bend relatively flat, two distinct bending regions were generally provided and were connected by a straight segment.